Field of the Invention
The present invention relates to a switching power supply device.
Description of Related Art
Conventionally, pulse width modulation (PWM) drive type switching power supply devices are generally and widely used as power supply devices of various applications.
The PWM drive type switching power supply device includes, as circuit elements constituting a voltage feedback loop thereof in general, an error amplifier arranged to generate an error voltage corresponding to a difference between an output voltage or a feedback voltage in proportion to the output voltage and a predetermined reference voltage, a slope voltage generating circuit arranged to generate a slope voltage, and a PWM comparator arranged to compare the error voltage with the slope voltage so as to determine an off-timing of the output transistor.
In addition, there is a conventional switching power supply device, which has a function of detecting a reverse current of an inductor current in a light load so as to forcibly turn off a synchronous rectifying transistor (so-called a reverse current cut-off function).
Note that an example of the conventional technique related to the above description is disclosed in Japanese Patent No. 4721905.
However, although the switching power supply device having the reverse current cut-off function can increase efficiency in a light load, it has a problem that a fluctuation range of the error voltage due to a rapid increase in load is large resulting in bad responsiveness to the load (the output voltage largely decreases from a target value).